This invention is an improvement in fencing structures and particularly an improvement in the woven or chain link fencing structures.
For over fifty years chain link fencing, after being woven, has been dipped in zinc to produce a galvanized coating. This galvanized coating inhibits the formation of rust.
During the last twenty years a far more enduring rust-preventative has been developed. This rust-preventative is a polymer coating for articles. One of the most effective ways of applying these polymer coatings is the use of powdered polymers in a fluidized bed. This technology has achieved widespread acceptance for coating a variety of articles.
Prior efforts to coat chain link fence have been frustrated by the fact that the chain link, in the fluidized bed, has had the adjoining links in contact with the result that the powdered polymers do not adhere to the entire surface of the chain link. Each such contact spot has proved a site for rust to develop and has caused the fence to deteriorate rapidly.
An effort to achieve the advantage of powdered polymer coating on chain link, while overcoming the above difficulty, has been made. This effort involved coating the single strand of wire prior to weaving it into the chain link. This approach has not worked because the wire must be repetitively cut into lengths about one and a half times the height of the fence. There will be bare ends of wire at both top and bottom approximately every two inches of fence line. Since this wire is exposed, rusting begins rather rapidly.
An effort has been made to overcome this problem by using galvanized wire prior to the polymer coating. This approach also has limitations because the exposed end, while rusting more slowly, will still rust and the galvanizing, which involves heating, lowers the strength of the wire forming the fence.
The coating of the entire chain link fence with no bare spots has long been recognized as a need in galvanizing operations. U.S. Pat. No. 1,623,593 to Harter, shows a system for compressing the links and thereby separating the points of contact after the chain has been dipped in the galvanizing bath. As is well known, molten zinc has very low viscosity and it will flow smoothly over adjacent metal as it comes out of a galvanizing bath.
A different method of achieving this result is shown in U.S. Pat. No. 2,933,410 to F. C. Brightly, Jr. Broadly, this patent discloses removing the chain link from the galvanizing bath, running it around a roller to break the welds caused by the solidified zinc, reintroducing the chain link to the galvanizing bath and withdrawing it again to assure uniform coating and no welding.
A simplified batch processing fluidized bed tank is disclosed in U.S. Pat. No. 3,807,355 to Newton N. Goldberg. A fluidized bed coating tank, in its simplest terms, blows air through a foraminous screen to heat thermosetting polymer particles to above their fusion temperature and the article to be coated is lowered into this apparent sea of floating warm particles. The particles adhere to the article at which point they polymerize and harden.
Another version of the fluidized bed is the electrostatic fluidized bed. This type of system is disclosed in U.S. Pat. No. 4,088,093 to Peter N. Y. Pan, in which a charge is placed on the article to be coated and the polymer is drawn to it both by the force of the air and the electric charge.
A particular type of this electrostatic fluidized bed is disclosed in U.S. Pat. No. 3,817,211, to Brown et al. This discloses a machine for coating a multi-filament strand in which the strands are mechanically separated by running them over a roller and the filaments are further separated by applying an electrostatic charge causing the fibers to repel each other. The thermosetting polymer is thus allowed to strike and adhere to each portion of the individual fibers rather than merely coating the periphery of the completed strand.